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SEATTLE — Authorities evacuated dozens of workers and set up a half-mile perimeter around part of the city’s port Wednesday after a bomb-sniffing dog indicated that two shipping containers from Pakistan could contain explosives.

By early evening, there was no sign of explosives and the port was preparing to resume normal operations, port spokesman David Schaefer said.

Customs agents used a “gamma-ray” device at Terminal 18, south of downtown, to peer through the containers’ steel walls and detected some items inside did not match the containers’ manifest, agency spokesman Mike Milne said.

The containers were checked by the bomb-sniffing dog. The dog reacted, and a bomb squad that searched the containers found nothing dangerous.

Officials said the containers were supposed to contain oily rags, which are often shipped internationally for recycling or use in packaging.

It was not immediately clear why the dog was mistaken.

Milne said the ship had originated in Hong Kong and made stops in China before arriving Monday in Seattle.

Terminal 18 covers nearly 200 acres, making it the port’s largest container terminal and one of the largest in the nation. It serves more than 20 steamship lines and receives more than 40 vessels each month.